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In this video, I wanted to show you how to use the lensometer. 

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The lensometer is a device used for checking prescription glasses

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and can be a little confusing. 

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The first step is, of course, to put 

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the glasses in the frames here, 

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and you can see this platform moves up and down. 

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And you want to put the optical center of this lens 

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such that it aligns here, 

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and this little brace holds the glasses in place. 

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You want to make sure both glasses 

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are touching the bottom of this platform. 

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Turn it on, and then look through this eye piece, 

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and this is what you should see. 

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Now, the hard part with using this machine 

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is you have to use two dials at the same time. 

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There's an axis dial up here 

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and there is a focus dial down here. 

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And you spin both of these and the goal 

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is to get the three small lines-- 

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the three little lines-- next to each other, 

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lined up and in focus. 

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So if we zoom in, we can see that there's three lines. 

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You want to get them lined up and in focus. 

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And then you can mark down what this is. 

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So if you look on our dial here and our focus, 

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we can see this is a 3.25 so that's the sphere. 

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The sphere is 3.25. 

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Now you move the focus in whatever direction it takes 

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in order to get the three fat lines in focus. 

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And the difference between those is your cylinder power. 

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So we went up +2.75 to get to 6.0. 

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So that's our cylinder +2.75.

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Our axis looks like it's about 12 degrees. 

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So here is our prescription. 

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Now, to get the bifocal power, 

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I need to move the glasses up to the bifocal segment 

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and see how much you need to change it 

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to get the three fat lines in focus again. 

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So we went from +6.0 to +8.5,

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 so our add is +2.50.